Pine oleoresin is mainly comprised of a series of unsaturated diterpene carboxylic acids, except turpentine, having a phenanthrene ring structure, a few neutral compounds, and a few fatty acids. These diterpene carboxylic acids have the same molecular formula C20H30O2, and are generally known as resin acids. The resin acids mainly include abietic acid, palustric acid, levopimaric acid, neoabietic acid, dehydrogenated abietic acid, pimaric acid, isopimaric acid, and sandaracopimaric acid, etc. These resin acids can be divided into two categories: abietic type resin acids and pimaric type resin acids by chemical structure. The molecule of abietic type resin acid has two conjugated double bonds and one isopropyl. Abietic acid, palustric acid, levopimaric acid, and dehydrogenated abietic acid all belong to this category.
The molecule of pimaric type resin acid has a methyl and a vinyl at the position of C13, and has two separate double bonds. This category mainly includes pimaric acid resin acids which are commonly seen in pine oleoresin and rosin, such as pimaric acid, isopimaric acid, sandaracopimaric acid, and other pimaric type resin acids which are rarely seen in the natural world, such as 8,15-isopimaric acid, Δ8(9)-pimaric acid, 7,15-pimaradiene-18-acid, etc.
Some components of pimaric type resin acids have biological activities against cancer, viruses, phlogosis, bacteria, and parasites, etc., and have potential therapeutic actions against diseases such as hypertension, tonic cystitis, allergic bronchitis, and chemical central nervous system disorders. They can also be transformed into derivatives by utilizing the active groups (e.g., carboxyl, exocyclic vinyl) in the molecular structure and can then be utilized again.
There are few reports on the research of the method for separation and preparation of some components in pimaric type resin acids:                (a) The following is a description of the alkali metal salt method [PALKIN S, HARRIS T H, The resin acids of American Turpentine Gum: The preparation of the pimaric acids from Pinus Palustris [J]. J Am Chem Soc, 1933, 55(9): 3677-3684; SANDERMANN W, Chemistry and Technology of Natural Resin, Turpentine, and Wood Pulp Oil Slick [M]. Beijing: China Forestry Publishing House, 1982:56]. In this method, pine oleoresin is treated by vacuum filtration first to obtain fresh resin acids, the resin acids are extracted with 80% ethanol, the residue of extraction is recrystallized with 95% ethanol to obtain the mixture of levopimaric acid and pimaric acid, and then the mixture is transformed into sodium salt which can be recrystallized to obtain pimaric acid. However, the yield of pimaric acid is only 3.3%. In this method, the temperature of extraction and crystallization must be controlled strictly, and pine oleoresin chosen as a raw material must ensure that the optical activity of sodium salt is higher than −160° C.        (b) The method reported by VESTERBERG A is: the crystallinic resin acid obtained from galipia officinalis resin or French rosin is first produced into pimaric ammonium salt, which is then transformed into pimaric sodium salt; finally, the pimaric sodium salt is recrystallized in 2% NaOH. However, the yield of this pimaric type resin acid is only 1.5% of galipia officinalis resin. In this method, pimaric acid experiences many transformation procedures; therefore, the loss is severe and the yield is low. This method is not suitable for large-scale preparation.        (c) The following is a description of the direct ammonium salt precipitation method [LOEBLICH V M, LAWRENCE R V, A new method for isolating isodextropimaric acid from pine oleoresin and rosin [J]. J Org Chem, 1958, 23(1): 25-26]. In this method, isopimaric ammonium salt is first precipitated directly from n-heptane solution of rosin with piperidine, then the ammonium salt is purified by fractional crystallization with 95% ethanol as the solvent, and finally, the ammonium salt is reduced to isopimaric acid. Although piperidine is selective to isopimaric acid, this method has a shortcomingin that the crystallization rate of the produced ammonium salt is very slow and the yield is low. Therefore, this method can only be used for research in small quantities.        (d) The flowing is a description of the method for preparing isopimaric acid. Recently, in Chinese Patent Application No. CN101302151A filed by ZHAO ZHENDONG, et al, a method for preparing isopimaric acid is disclosed. In this method, thermally isomerized rosin is dissolved in acetone, and treated with isobutanolamine to form a crude product of isopimaric ammonium salt. The isopimaric ammonium salt is purified by the multi-recrystallization method, then treated with acidification and ionization via hydrochloric acid, and finally refined and purified to obtain purified isopimaric acid. Although this method has advantages such as low cost and high yield, it is not suitable for preparing mixed pimaric type resin acids.        (e) The following is a description of the maleated derivatization method [HARRIS G C, SANDERSON T F. Rosin acids (III) The isolation of dextropimaric acid, a new pimaric-type acid, isodextropimaric acid [J]. J Am Chem Soc, 1948, 70(1): 2079-2085; ALDRICH P H, Process for separation of rosin adducts from mixtures with rosin: U.S. Pat. No. 3,562,243 [Patent], 1971]. In this method, ammonium salt is produced from the reaction between cyclohexylamine and resin acids; the ammonium salt is treated by crystallization, separation, and acidification to obtain a purified resin acid mixture; the resin acid mixture is catalyzed by saturated hydrogen chloride to react with maleic anhydride in benzene solvent under boiling conditions for 24 hours; after the benzene solvent is distilled, the residue is dissolved in concentrated alkaline solution; the pH of the solution is adjusted to 6.2 in order to make the unreacted resin acid crystallize; the unreacted resin acid reacts with butanolamine (2-amido-2-methyl-1-propanol) in acetone solution to obtain the crystalline of isopimaric ammonium salt; and finally the isopimaric ammonium salt is recrystallized with methyl acetate and treated by acidification, ionization, and purification to obtain isopimaric acid. ALDRICH et al studied several processes for separating maleated adducts, including crystallization with glacial acetic acid, dissolution and separation of carbon tetrachloride adduct, and dissolution by means of solvent polarity difference, etc. The target product of the above method is the isopimaric acid. One of the shortcomings of this method is long reaction time. Another shortcoming of this method is the difficulty in completely separating maleopimaric acid and unreacted resin acids, including pimaric type resin acids, dehydro abietic acid, and a small amount of abietic acid-type resin acid that is not thoroughly reacted, and the resulting product may contain maleopimaric acid. Moreover, wide use of benzene solvent and hydrogen chloride gas may cause serious environmental pollution and high requirements for the equipment.        (f) The following is a description of the benzoquinone derivatization method [SANDERMANN W, Chemistry and Technology of Natural Resin, Turpentine, and Wood Pulp Oil Slick [M]. Beijing: China Forestry Publishing House, 1982: 56]. In this method, the resin acids from pine resin are transformed into benzoquinone adducts which are then filtered, and the crystalline product obtained from the mother solution is crystallized in acetone and then recrystallized in both glacial acetic acid and methanol to obtain pimaric type resin acids. A drawback of this method is that the application approaches of the benzoquinone adducts are very limited, and therefore may cause loss of raw material and increased cost. This method needs further improvements in terms of economic efficiency.        (g) The following is a description of the rectification method [HARRIS G C, SANDERSON T F, Rosin acids (III) The isolation of dextropimaric acid, a new pimaric-type acid, isodextropimaric acid [J]. J Am Chem Soc, 1948, 70(1): 2079-2085]. In this method, fatwood rosin or gum rosin is rectified in a tower having 10 tower plates at 13.3 Pa pressure; the fraction with the boiling point between 136° C.-200° C. is taken to produce ether solution of sodium salt; the sodium salt is treated by acidification and the resin acids are dissolved in ether; and then, ether is removed to obtain concentrated pimaric acids and isopimaric acids. The drawbacks of this method include the high requirements for fractionation condition, which are adverse to operation, and the low yield of isopimaric acids and pimaric acids.        
At present time, there is limited research and development on separation and purification of pimaric type resin acids in the world, and no published report on developing and utilizing pimaric type resin acids as a product. Nor is there any production of commercial pimaric type resin acid product or rosin product rich in pimaric type resin acid. Exploring high-efficiency, high-yield, and high economic feasibility methods for preparation of pimaric type resin acids will be beneficial to facilitate and speed up both the research and development of pimaric type resin acid products, especially in the application of medicine, biology, material, and other fields.